Shorting system for radio coils



Jan. 10, 1950 J. L. BOWDEN 2,493,746

SHORTING SYSTEM FOR RADId COILS Filed Aug. 5, 1945 2 Sheets-Sheet 2 F/6f6. F/s.7.

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Patented Jan. 10, 1950 UNITED STATES PATENT OFFICE I sHoRTINc-sY-s'rnM FOR RADIO COILS John LrBowiden, United States Army Application August 3,1945, Serial No. 608,828

7 2 Claims. (01. 171-242 (Granted under the act of March 3, 1883, as amended Afllil' 30, 1928; 370 0. G 757) The invention described hereinmay be manu- Tactured and used by or for the Government fo governmental purposes, without the payment of any royalty thereon.

This invention relates to an improved switch means for varying the tank circuit inductance in radio transmitters.

The invention described herein is particularly adapted'for use in amplifier stages of radio trans- "mitters. This switch has been found particularly useful in the 'Army Net Control Radio Station WAR, Fort Myer, Virginia, where it is now extensively used in the place of prior art systems found to have serious'disadvantages. In the prior art it is known that a shorting bar may be placed across the taps to be shorted, but this has the disadvantage in that much time is spent in changing from one length of the bar to another, making it necessar to change by use of a wrench. At the same time the changing from one length of the bar to another causes the coil to sag and change its shape. Large transmitters used by the Army and commercially adapted to operate over a wide frequency spectrum have used various means of shorting inductance of cells, but no switch or 'coil shorting method exce t the present invention has been used that is entirely satis-- factory.

Figure 1 illustrates a side view of one -embodiment'of my invention.

Figure 2 shows the relative arrangement of'the shaft and the several switch blades constituting the inventive part of Figure 1.

Figure 3 illustrates a preferred form of my invention in perspective; the details of the pushpull transmitter circuit being omitted.

Figure 4 illustrates a single ended transmitter incorporating the invention.

Figure 5 shows a push-pull amplifier circuit incorporating the invention.

Figure 6 shows another push-pull amplifier circuit incorporating the invention.

Figure '7 shows a push-pull amplifier of a pinetwork incorporating the invention.

In Figure 3 is shown an improved form of my invention. This figure shows the main tank coil I00 of a push-pull radio transmitter. This coil is solely supported by the leads thereto as will later appear in connection with Figure 2. The coil I00 has taps lIlI, I02, I03, I04, I05, I06, I01, I08, I09, H0, III, and H2 on successive turns thereof. These taps are in the form of contact plates and project vertically downward from the tank can and between the switch blades mounted r 2 on the shaft I I3. For example, switch blades I I4 and-H5 are on opposite sides of contact bar IOI. Similarly switch blades H6 and Ill are on opposite sides of contact bar I02; while the switch blades I I8 and H9 are on opposite sides of contact bar I03.

Switch blades H4 and H5 have a segmental angle of approximately 45 degrees. Switch blades HS and H1 are similar to blades H4 and H5 except they have a somewhat larger segmental angle, for example 99 degrees. The same may be said for switch blades I I8 and H0 except they have a segmental angle of approximately 153 degrees. The same may be said for switch blades I20 and I2I except they have a segmental angle of approximately 207 degrees. The same may be said for switch blades I22 and I23 except they have a segmental angle of approximately 261 degrees, and the same may be said for switch blades I24and. I25 except they have a segmental angle of 215 degrees. The segmental angle of switch blades I26 and I21 is the same as that of blades I24 and I25. Switch blades I23 and I21 are the same as I24 and I25; the blades I28 and I29 are the same as those of I22 and I23; the blades I30 and I3I are the same as I20 and I2I; the blades I32 and I33 are the same as H8 and H9; the blades I34 and I35 are the same as H6 and I11; the blades I36 and I31 are the same as blades H4 and H5.

The shaft 113 at its rear end has a cam I40 having a latch I41 pivoted at I42 and held in place by a pull spring I43. When the shaft I I3 is rotated latch MI engages the slots in cam I40 and holds the shaft in the several positions in which it is desired for the apparatus to operate.

When the shaft H3 is in the position shown, bars IOI through II2 inclusive are all connected together by the switch blades II through I31 inclusive and therefore only those turns of the coil I 00' which are at the two ends thereof are notshorted and are the only turns effective in creating inductance from the main tank coil. However, when it is desired to change the frequcncy 'of the transmitter to a different band the shaft H3 may be rotated clockwise to its next position in which switch blades H4 and [I5 disengage bar I M and switch blades I 36 .and I31 disengage bar II2. Therefore, two additional turns of the tank coil are effective in introducing inductance into that tank coil. In the third position of clockwise rotation of shaft H3 all of the following switch blades are disengaged from their respectivecontactor bars H4, I15, H6, H1, I34,

I35, I36, and I31. Therefore additional turns of the main tank coil at the opposite ends thereof become effective in introducing inductance into the main tank circuit. For example, when the switch is rotated clockwise to the next operative position the following switch blades are not in contact with their respective contacter bars H4, H5, H6, H1, H8, H9, I32, I33, I34, I35, I36 and I31. Therefore, additional turns of the main tank coil become effective at the opposite ends thereof in introducing inductance into themain tank circuit.

Referring particularly to Figure 1 coil I3 is shown with its supporting copper tubes II and I2. By means of tubes II and I2 coil I3 may be mounted directly to a conventional tank circuit,

condenser. Coil I3 is a helical copper tube with a tap at its center I4. f

The coil I3 constitutes the main plate tank circuit of the final push-pull amplifier of a radio transmitter. In order to provide for push-pull operation of the amplifier, the coil I3 is tapped in its center at I4, the tap I4 being suitably connected in the push-pull amplifier circuit. Three turns from the left end of the coil I3 is a tap I6 and similarly, three turns from the right end of coil I3 is a tap I1, five turns from the left end of the coil I3 is a tap I8 and five turns from the right end of the coil I3 is a tap I9, seven turns from the left end of coil I3 is a tap 20, and seven turns from the right end of the coil I3 is a tap 2I. It is understood that the location of each of the taps recited above is optional and more or less taps suitably positioned on the coil may be used without departing from the principle and mode of operation of the invention described herein.

There is provided a supporting metal frame work 35 fixed at its lower end so that it and the condenser to which it may be fastened constitute the sole support for coil I3. Mounted on the metal frame work 35 and insulated therefrom are the several switch contacts 22, 23, 24, 25, 26 and 21 which respectively electrically connect with the several copper tubing leads I6, I1, I8, I9, 20 and 2|. The leads I6 to 2I inclusive are supported by the metal frame work 35, although in sulated therefrom, and these several leads help in the support of the coil I 3. Mounted on the shaft 34, which is carried by the metal frame work 35 are the switch blades 28, 29, 30, 3I, 32, and 33 which are adapted to respectively engage and disengage the several switch contacts 22, 23, 24, 25, 26 and 21 as will hereinafter appear.

The shaft 34 carries a dial 36 which is adapted to be rotated to four distinct positions, numbered 1, 2, 3, and 4 on the dial. The several positions are indicated by the pointer 38A. Supported by the frame work 35 is a spring element 31 which is adapted to engage the cam 38 to hold the shaft 34 in the said several four distinct positions in a well known way. The notches in the cam 38 are so positioned that when the dial 36 is turned to position 1 as indicated by the pointer 38A, none of the several switch blades 28, 29, 30, 3 I, 32 or 33 are in engagement with any of the switch contacts 22, 23,24, 25,26 and 21.

However, when the dial 36 is rotated to position 2 as indicated by the pointer 38A on the dial 36, all of the switch blades 28, 29, 30, 3I, 32 and 33 are in engagement with their respective complimentary switch contacts 22, 23, 24, 25, 26 and 21, In this position all of the coil I3 between the tap l6 and the tap I1 is shorted out, leaving 4 only a small portion of the coil in the circuit and thereby causing the push-pull radio transmitter to operate at a high radio frequency, in contrast to the low frequency that is obtained when the dial 36 was in position 1 as indicated by the pointer 38A.

When the dial 36 is rotated to position 3 as indicated by the pointer 38 on the dial 36, switch blades 28 and 29 are no longer in contact with their respective complimentary switch contacts 22 and 23. However, switch blades 30, 3|, 32, and 33 are in engagement with their respective switch contacts 24, 25, 26 and 21. Hence, the coil I3 is shorted between the tap I8 and the tap I9. Thus in position 3 the frequency at which the radio transmitter operates is lower than the frequency at which it operated when the dial 36 was in position 2.

When the dial 36 is rotated to position 4 as indicated by the pointer 38, only the switch blades 32 and 33 are in engagement with switch contacts. In this position switch blades 32 and 33 are in contact with switch contacts 26 and 21 but switch blades 26, 29, 30 and 3| are not in contact with any switch contact and, therefore, only that portion of the coil I3 which is between the tap 20 and the tap 2! is shorted out. Hence, the effective portion of the coil I3 includes all of that from the left end to tap 20 and all of that beyond tap 20 and 2| to and inclusive, to the right end of coil I3.

It is apparent from this invention that when turns of the coil are being shorted out a wiping contact of the switch blades is employed. This has the advantage that the switch blades are constantly kept clean during operation of the switch. Furthermore, by using this invention and particularly segments of the circle as switch blade elements it is possible as more turns are shorted out and the inductance is changed to keep the unused portion of the coil shorted at several points preventing voltages from building up between the turns.

The switch induces a minimum of stray capacity and is designed to make the circuit balanced from the lowest to the highest frequency. The switch can be adapted for use on both singleended and push-pull amplifiers.

Figure 4 shows the device of the invention used in connection with a single-ended transmitter. The main tank coil 50 of the transmitter is successively shorted by the switch blades 5|, 52 and 53 as the switch is rotated from the open position 4 through positions 1, 2 and 3. The adaptation of the invention to the single-ended amplifier is clearly obvious when taken in connection with the foregoing description of the invention in connection with a push-pull transmitter.

Figure 5 shows the device of Figure 2 as connected to a conventional push-pull amplifier.

Figure 6 illustrates the invention as applied to a push-pull amplifier shorting taking place first at the ends of the tank coil instead of in the middle thereof. In Figure 6 the shape of the several switch segments is such that in the 3rd position no shorting whatsoever takes place. In position 2 segments short leads Gil-6| and 1Il.1I. In position 1 the switch segments short the leads Ell-BI and 62 and 10-1I and 12.

In Figure '1 there is shown a push-pull amplifier with a pi-network. Two switches are employed for each tank coil. The two switches and BI are ganged. together with the shaft 82. The tank coils 83 and 84 are shorted to a greater or lesser extent by the switches 80 and 04. Switches 80 and 84 are constructed in similar fashion to the switch of Figures 2 and 3 except configuration of the segments is such that as the switch is progressively rotating a greater amount of the two coils are shorted.

When shorting in a push-pull amplifier, one switch can be used if the shorting is done from the center of the coil to the hot portion (as shown in Figure 2) but if the shortin is done from the hot end of the coil to the cold two switches will be required as shown in Figure 6. In the form shown in Figure 6 the switches must be connected by an insulating shaft such as 65.

The switch principle can be used in constructing switches for extremely low power tank circuits or for transmitters employing many kilowatts of power. The principle of the invention renders the system extremely efficient due to its low resistance, low capacity and the physical size in comparison with previous band changing systems of equal flexibility.

I claim to have invented:

1. In a radio transmitter, a main helical tank coil, first and second taps thereon equally spaced from the center of such coil and on opposite sides of said center, third and fourth taps on said coil equally spaced from the center of such coil and respectively on opposite sides of said center and farther therefrom than the first and second taps, fifth and sixth taps on said coil equally spaced from the center of such coil and respectively on opposite sides of said center and farther therefrom than the third and fourth taps, each of said taps including conducting means electrically and mechanically attached to the coil and extending a short distance therefrom, and rotary switch means comprising six segmental switch blades of conducting material which respectively are arranged to engage and disengage said taps respectively, the first and second blades having a large segmental angle and engaging said first and second taps throughout said angle, the third and fourth blades having a segmental angle smaller than that of the first and second blades and engaging said third and fourth taps, the third and fourth blades being so positioned as respect the first and second blades that when the third and fourth blades engage the third and fourth taps respectively that the first and second blades engage the first and second taps respectively, said fifth and sixth blades having smaller segmental angles than that of the third and fourth blades and engaging said fifth and sixth taps throughout such small angle, the fifth and sixth blades being so related to the first, second, third and fourth blades that whenever the fifth and sixth blades engage the fifth and sixth taps respectively that the first, second, third and fourth blades are respectively in engagement with the first, second, third and fourth taps.

2. In a radio transmitter, a helical main tank coil, first and second taps on said coil equally spaced from the center thereof and on opposite sides of said center, third and fourth taps on opposite sides of the center of said coil and equally spaced from said center and farther from said center than the first and second taps, said taps constituting short electrical bars extending from said coil, a rotatable shaft parallel to the center line of said helical tank coil and positioned near said taps, and first, second, third and fourth switch blades mounted on said shaft and in engagement with said first, second, third and fourth taps respectively, said switch blades having leading edges parallel to each other and the third and fourth switch blades having a smaller segmental angle than the first and second blades, whereby the inner turns of the coil are shorted whenever the more removed turns of the coil are shorted.

JOHN L. BOWDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

